Before she decided to bar former President Donald J. Trump from Maine’s primary ballot, Shenna Bellows, the secretary of state, was not known for courting controversy.
She began her career in public office as a state senator in 2016, winning in a politically mixed district. She prided herself on finding common ground with Republicans, an approach she said was shaped by growing up in a politically diverse family.
As the former head of the state’s American Civil Liberties Union, Ms. Bellows did not shy away from divisive issues. But her ballot decision on Thursday was perhaps the weightiest and most politically fraught that she had faced — and it sparked loud rebukes from Republicans in Maine and beyond.
In an interview on Friday, Ms. Bellows defended her decision, arguing that Mr. Trump’s incitement of the Jan. 6, 2021, attack on the U.S. Capitol made it necessary to exclude him from the ballot next year.
“This is not a decision I made lightly,” Ms. Bellows, 48, said. “The United States Constitution does not tolerate an assault on the foundations of our government, and Maine election law required that I act in response.”
Ms. Bellows, a Democrat, is among many election officials around the country who have considered legal challenges to Mr. Trump’s latest bid for the White House based on an obscure clause of the 14th Amendment that bars government officials who have engaged in “insurrection” from serving in the U.S. government.
The ban, which is being appealed in the courts, made Maine the second state to disqualify Mr. Trump from the primary ballot next year. Colorado’s Supreme Court ruled last week that his efforts to remain in power after the 2020 election were disqualifying. Opponents of Mr. Trump are pursuing similar challenges in several other states.
Lawyers on both sides of the dispute are calling on the U.S. Supreme Court to promptly issue a ruling on how election officials should interpret the insurrectionist clause of the 14th Amendment, which was adopted to bar Confederate officials from serving in the U.S. government after the Civil War.
Mr. Trump’s campaign and Maine Republicans have called Ms. Bellows’s decision an overreach. The Maine Republican Party issued a fund-raising appeal that called Ms. Bellows “a biased Democrat Party hack unworthy of the high office she holds.”
Maine’s two senators, Susan Collins, a Republican, and Angus King, an independent who generally votes with Democrats, also took issue with the ban, with Mr. King saying that “the decision as to whether or not Mr. Trump should again be considered for the presidency should rest with the people as expressed in free and fair elections.”
Ms. Bellows said it was not uncommon for secretaries of state to bar candidates from the ballot if they did not meet eligibility requirements, and noted that she refused to allow Chris Christie, the former governor of New Jersey, to appear on the state’s Republican primary ballot after he failed to get enough signatures.
Ms. Bellows, who became a powerful figure in a politically divided state, said she had managed to work collaboratively with Republicans. Though in interviews, longtime colleagues of Ms. Bellows said they were not surprised by her willingness to take a politically risky stance.
“Secretary Bellows has a well-earned reputation for being an extremely hard worker who is willing to follow her conscience,” said Zach Heiden, the chief counsel at the A.C.L.U. in Maine who reported to Ms. Bellows when she led the organization from 2005 to 2013.
At the A.C.L.U., Ms. Bellows championed same-sex marriage and expanding voting rights, and fought provisions of the Patriot Act and certain government surveillance programs after the Sept. 11 attacks. In 2014, after leaving the organization, Ms. Bellows launched an unsuccessful bid to unseat Ms. Collins, who has been in the Senate since 1997.
“At first the Democratic establishment did not take her seriously,” said John Brautigam, a former Maine lawmaker. “But Shenna won the nomination and conducted a credible and issue-focused campaign.”
In 2016, Ms. Bellows won a State Senate seat that included her hometown, Manchester. The district is politically mixed: It favored Barack Obama in 2008 and 2012, and Mr. Trump in 2016.
While her politics have been decidedly liberal, Ms. Bellows said she had never seen herself as an extreme partisan. Shortly after becoming a state senator, Ms. Bellows said she found common ground with Republicans on several initiatives, including a bill making it easier to license medical professionals in the state.
That approach to politics, she said, was shaped by growing up in a family that was politically split.
“The key to my success in working across the aisle has always been the willingness to listen and hear both sides and to be open to what people have to say,” she said.
In 2020, Ms. Bellows put herself forward as a candidate for secretary of state, a role that is chosen by the Legislature in Maine. Ms. Bellows said she sought the position because she saw it as an opportunity to safeguard democratic principles, key among them the right to vote.
“As a kid, I had a copy of the Bill of Rights on my bedroom wall,” she said. These days, she said, she often carries a copy of the U.S. Constitution in her purse.
The aftermath of the 2020 election deeply disturbed Ms. Bellows, who condemned Mr. Trump in posts on social media after an effort to impeach him failed.
“He should have been impeached,” she wrote in February 2021. “But history will not treat him or those who voted against impeachment lightly.”
Republicans have said that those remarks call into question her objectivity. But Ms. Bellows said her decision to remove Mr. Trump from the ballot was based solely on the facts and the law. She said a motto from her time at the A.C.L.U. had long guided her actions.
“We had a saying: There are no permanent friends, no permanent enemies, just permanent principles,” she said. “That is a philosophy that I try to live my life by.”